In one example, villagers who agree to protect the trees instead of cutting them down for farming or fuel can receive money and training in sustainable livelihoods.

Marriott's $2 million is a start, and the company may raise more from featuring the reserve on its website, offering customers a chance to offset the greenhouse gases emitted during their travel.

"We decided to be a leader in this space," Marriott Executive Vice President Arne M. Sorenson said. "It makes us a better brand and increases customer loyalty."

Some environmental groups, including Greenpeace and Friends of the Earth, oppose the use of credits by corporations. Coal-fired power plants and other major emitters of greenhouse gases should clean up their own smokestacks, they contend, rather than be permitted to buy their way out of complying with emission caps through forest credits that are difficult to quantify.

But others believe that governments and charities alone won't be able to finance forest preservation. Norway has pledged $1 billion to Amazon projects, but tens of billions of dollars more would have to come through corporate trading after countries place firm caps on greenhouse gases.

Meanwhile, U.S. climate legislation remains stalled in the Senate. If Congress fails to pass a bill this year, some of the first American corporate money could flow through California's cap-and-trade program, set to take effect in 2012. Delegations of California climate officials have visited Juma and other Amazon projects.